Having Apple do it, may provide some additional coverage for some period of time as they will cover the repair. If you have Applecare and/or are still within your first year since purchasing your phone, Applecare will cover the repair. Apple actually will just replace your iPhone with a refurb. It is probably cosmetically in great shape.
For service or support questions including existing order status, call: Customer Support: 1-800-331-0500
Information on iPhone unlocking can be found here by copying this link into your browser: https://www.att.com/deviceunlock/client/en_US/